Driving circuit, method for driving a MEMS gyroscope and a corresponding MEMS gyroscope

ABSTRACT

A driving circuit for a microelectromechanical system (MEMS) gyroscope operating based on the Coriolis effect is provided. The driving circuit supplies drive signals to a mobile mass of the MEMS gyroscope to cause a driving movement of the mobile mass to oscillate at an oscillation frequency. The driving circuit includes an input stage, which receives at least one electrical quantity representing the driving movement and generates a drive signal based on the electrical quantity; a measurement stage, which measures an oscillation amplitude of the driving movement based on the drive signal; and a control stage, which generates the drive signals based on a feedback control of the oscillation amplitude. The measurement stage performs a measurement of a time interval during which the drive signal has a given relationship with an amplitude threshold, and measures the oscillation amplitude as a function of the time interval.

BACKGROUND Technical Field

The present invention relates to a driving circuit and a driving methodfor a MEMS gyroscope, in particular a MEMS gyroscope operating on thebasis of the Coriolis effect, the so-called CVG (Coriolis VibratingGyroscope). The present invention further relates to a correspondingMEMS gyroscope.

Description of the Related Art

As is known, current micromachining techniques enablemicroelectromechanical systems (MEMS) to be obtained starting fromlayers of semiconductor material, which have been deposited (e.g., alayer of polycrystalline silicon) or grown (e.g., an epitaxial layer) onsacrificial layers, which are then removed via chemical etching.Inertial sensors, in particular accelerometers and gyroscopes, obtainedwith this technology are encountering a growing success, for example inthe automotive field, in inertial navigation, and in the field ofportable devices.

In particular, integrated gyroscopes of semiconductor material madeusing MEMS technology are known, operating on the basis of therelative-acceleration theorem, exploiting Coriolis acceleration. Aspreviously mentioned, these MEMS gyroscopes are referred to as CVGs.

When a rotation at a certain angular velocity (the value of which is tobe detected) is applied to a mobile mass (the so-called inertial mass)of the MEMS gyroscope, which is driven at a linear velocity, theinertial mass feels an apparent force, defined as the Coriolis force,which determines a displacement thereof in a direction perpendicular tothe direction of the driving linear velocity and to the axis about whichthe rotation occurs.

The inertial mass is supported via elastic elements that enable itsdisplacement in the direction of the apparent force. On the basis ofHooke's law, the displacement is proportional to the apparent force, sothat from the displacement of the inertial mass it is possible to detectthe Coriolis force and thus the value of the angular velocity of therotation that has generated it.

The displacement of the inertial mass may, for example, be detectedcapacitively, determining, in a condition of resonance oscillation (soas to maximize the amplitude of the movement), the variations ofcapacitance caused by the movement of mobile sense electrodes, which arefixed with respect to the inertial mass and are capacitively coupled tofixed sense electrodes (for example, in the so-called “parallel-plate”configuration, or else in the so-called “comb-fingered” configuration).

FIG. 1 shows schematically, and purely by way of example, a possibleembodiment of a known type of a MEMS CVG, designated as a whole by 1, inthis case of the uniaxial type, i.e., being able to detect an angularvelocity, for example an angular velocity Ω_(z), acting along a singlesensing axis, in the example acting about a vertical axis z.

The MEMS gyroscope 1 comprises a micromechanical structure 1′ having adriving mass 2, with main extension in a horizontal plane xy. Thedriving mass 2 is coupled to a substrate S (illustrated schematically)via anchorages 3, to which it is connected by elastic anchorage elements4, which are configured to enable a driving movement of the driving mass2 along a first horizontal axis x of the aforesaid horizontal plane xy.

Drive electrodes 5 and drive-sense electrodes 6 are coupled to thedriving mass 2 and include respective mobile electrodes, coupled to thedriving mass 2, and respective fixed electrodes, fixed with respect tothe substrate, the mobile electrodes and the fixed electrodes beingcapacitively coupled in the so-called comb-fingered configuration.

The drive electrodes 5 are biased by drive (or excitation) signals D₁,D₂ so as to generate, as a result of the electrostatic coupling betweenthe respective mobile electrodes and the respective fixed electrodes,the aforesaid driving movement of the driving mass 2, in particular aresonant movement at an oscillation frequency f_(d) (which correspondsto the natural frequency of oscillation of the micromechanical structure1′), and the drive-sense electrodes 6 enable generation of drive signalsI₁, I₂, in particular capacitive-variation signals indicative of theextent of the driving movement, i.e., of the amplitude of oscillation ofthe driving mass 2. The drive signals I₁, I₂ are advantageously of adifferential type, i.e., having opposite variations in response to thedriving movement. As illustrated in FIG. 1 , a first set of drive-senseelectrodes, designated by 6′, is in fact configured to generate a firstcapacitive variation, due to the driving movement, and a second set ofdrive-sense electrodes, designated by 6″, is configured to generate asecond capacitive variation, opposite to the first capacitive variation,due to the same driving movement.

The micromechanical structure 1′ of the MEMS gyroscope 1 furthercomprises an inertial mass 8, elastically coupled to the driving mass 2,by elastic coupling elements 9, configured so that the inertial mass 8is fixedly coupled to the driving mass 2 during the driving movement,thus being drawn along the first horizontal axis x, and is further freeto move in a sensing movement along a second horizontal axis y of thehorizontal plane xy, orthogonal to the first horizontal axis x, as aresult of the Coriolis force that is generated in the presence of theangular velocity Ω_(z) acting about the vertical axis z, orthogonal tothe aforesaid horizontal plane xy.

Sense electrodes 10 are coupled to the inertial mass 8, capacitivelycoupled together in comb-fingered configuration, in part coupled to theinertial mass 8 and in part fixed with respect to the substrate so as togenerate differential capacitive variations due to the sensing movement.

The sense electrodes 10 thus enable generation of sense signals V_(s1),V_(s2), in particular capacitive-variation signals representing theextent of the sensing movement, i.e., the amplitude of the oscillationof the inertial mass 8 along the second horizontal axis y, which may beappropriately processed for determining the value of the angularvelocity Ω_(z) to be detected.

In particular, the MEMS gyroscope 1 comprises: a sense, or read, circuit12, coupled to the sense electrodes 10 and configured to generate anoutput signal, for example an output voltage V_(out), as a function ofthe sense signals V_(s1), V_(s2); and a driving circuit 14, coupled tothe drive electrodes 5 and to the drive-sense electrodes 6 andconfigured to generate the drive signals D₁, D₂ by a feedback controlbased on the drive signals I₁, I₂ and a desired oscillation amplitude ofthe drive mode (the value of this amplitude being determined at thedesign stage so as to ensure the desired sensitivity in the detection ofangular velocities).

Indeed, it is known that the oscillation amplitude of the drive mode inthe MEMS gyroscope 1 is to be accurately controlled, given that itsvalue directly determines the sensitivity characteristics of the sensorin the detection of angular velocities.

It should be noted that the driving mass 2 and the inertial mass 8 arebiased at a constant voltage, designated by V_(ROT) in FIG. 1 and in thesubsequent figures.

In greater detail and as illustrated in FIG. 2 , the driving circuit 14,in an embodiment of a known type, has: a first input 14 a and a secondinput 14 b, configured to receive the aforesaid drive signals I₁, I₂;and a first output 14 c and a second output 14 d, configured to supplythe aforesaid drive signals D₁, D₂.

The driving circuit 14 comprises an input stage 15, which is coupled tothe first input 14 a and to the second input 14 b and is configured tosupply a drive signal V_(SD), in particular a differential-voltagesignal, as a function of the drive signals I₁, I₂. The input stage 15is, in the example, a capacitance-to-voltage (C2V) converter, configuredto generate, as a function of the capacitive-variation signals receivedat the input, and of corresponding current signals i_(SD), a voltagesignal at the output. Different embodiments may, however, be envisagedfor the aforesaid input stage 15, which could, for example, comprise atransimpedance amplifier.

In particular, if the Barkhausen criteria is satisfied for the driveloop, the drive signal V_(SD) is a sinusoidal signal at the naturaloscillation frequency f_(d) of the driving section of themicromechanical structure 1′ of the MEMS gyroscope 1.

The driving circuit 14 further comprises: a comparator stage 16, whichreceives at its input the drive signal V_(SD) and generates at itsoutput (by zero-crossing detection) a clock signal ck at the oscillationfrequency f_(d) (referred to as “natural clock”); and a PLL(Phase-Locked Loop) stage 17, which receives at its input the naturalclock signal ck and generates at its output an appropriate number ofderived clock signals ck, at frequencies that are appropriately linkedto the oscillation frequency f_(d) and which are used in a known mannerwithin the MEMS gyroscope 1, for example for the operations performed bythe same driving circuit 14 and sensing circuit 12.

The driving circuit 14 further comprises an automatic-gain control (AGC)stage 18, which receives at the input the drive signal V_(SD) and areference signal V_(ref), which is indicative of the desired (orby-design) oscillation amplitude of the drive mode.

The AGC stage 18 generates, as a function of the drive signal V_(SD) andof the reference signal V_(ref), a control signal V_(ctrl), which is afunction of the difference between the same drive signal V_(SD), forexample between its peak value, and the reference signal V_(ref).

The driving circuit 14 further comprises a forcing stage 19, which iscoupled to the first output 14 c and to the second output 14 d of thedriving circuit 14, further receives an appropriate derived clock signalck from the PLL stage 17 and the aforesaid control signal V_(ctrl) fromthe AGC stage 18, and is configured to generate the drive signals D₁, D₂as a function of the same control signal V_(ctrl).

The driving circuit 14 thus implements a feedback control so as to forcethe value of the drive signals D₁, D₂ to be such as to cause the drivesignal V_(SD) to have a desired relation with the reference signalV_(ref) (and so as to obtain, as a result, the desired oscillationamplitude of the driving movement).

The present Applicant has noticed that the aforesaid driving solutionhas some problems, at least in certain operating conditions.

In the first place, the AGC stage 18, by its purely analog nature, isaffected in a non-negligible way by possible variations (mismatch) ofthe values of the circuit components, for example due to manufacturingprocess spread, ageing, or external parameters, such as temperature orhumidity. Consequently, it is possible for undesirable variations tooccur in the control of the amplitude of oscillation of the drive modeand, thus, undesirable variations of the detection sensitivity of theMEMS gyroscope 1 with respect to angular velocities.

Furthermore, once again due to the AGC stage 18 (which comprises, in aknown way, amplification blocks that have to be appropriately biased),the driving circuit 14 has a considerable electrical consumption, whichhas a marked effect on the overall consumption of the MEMS gyroscope 1.

BRIEF SUMMARY

An improved driving solution for a MEMS gyroscope is provided.

According to the present solution, a driving circuit for a MEMSgyroscope and a corresponding driving method are consequently provided.A driving circuit for a MEMS gyroscope is provided. The driving circuitincludes an input stage configured to receive at least one electricalquantity indicative of a driving movement of a mobile mass of the MEMSgyroscope, and generate at least one drive signal based on theelectrical quantity. The driving circuit includes a measurement stageconfigured to determine a duration of a time interval in which the drivesignal satisfies a given relationship with an amplitude threshold, anddetermine an oscillation amplitude of the driving movement based on theduration of the time interval. The driving circuit includes a controlstage configured to receive the oscillation amplitude, generate drivesignals for a mobile mass of the MEMS gyroscope based on the oscillationamplitude, and supply the drive signals to the mobile mass of the MEMSgyroscope to cause the driving movement to be at an oscillationfrequency.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present invention, preferredembodiments thereof are now described, purely by way of non-limitingexample and with reference to the attached drawings, wherein:

FIG. 1 shows a schematic and simplified representation of a MEMSgyroscope, of a known type, and of the corresponding micromechanicalstructure;

FIG. 2 is a general block diagram of a driving circuit of the MEMSgyroscope, which is also of a known type;

FIGS. 3-6 show plots of electrical quantities of a driving circuit of aMEMS gyroscope according to the embodiments described herein;

FIG. 7 is a block diagram of the driving circuit of the MEMS gyroscopeaccording to a first embodiment;

FIG. 8 shows further plots of electrical quantities in the drivingcircuit;

FIG. 9 is a block diagram of the driving circuit of the MEMS gyroscopeaccording to a further embodiment; and

FIG. 10 is a general block diagram of an electronic device in which theMEMS gyroscope is used according to a further aspect of the presentapplication.

DETAILED DESCRIPTION

As will now be discussed in detail, an aspect of the present applicationenvisages measuring the oscillation amplitude of the driving movement bya time-domain measurement of a substantially digital nature, inparticular based on measurement of a time interval during which thedrive signal V_(SD) (see the foregoing discussion) has a given relationwith an appropriate amplitude threshold.

The drive signal V_(SD), of a sinusoidal type, which, as it has beendiscussed previously, represents the main vibration mode associated tothe driving movement, may be expressed as:V _(SD) =A ₀ sin(2πf _(d) t)where f_(d), as mentioned previously, is the oscillation frequency, andA₀ is the oscillation amplitude of the driving movement.

Referring also to FIG. 3 , it may be shown that the time interval Δtduring which the drive signal V_(SD) is greater than an amplitudethreshold A_(th) may be expressed as:

${\Delta\; t} = {{\frac{T_{d}}{2} - {2\frac{1}{2\pi\; f_{d}}{\sin^{- 1}( \frac{A_{th}}{A_{0}} )}}} = {\frac{1}{f_{d}}\lbrack {\frac{1}{2} - {\frac{1}{\pi}{\sin^{- 1}( \frac{A_{th}}{A_{0}} )}}} \rbrack}}$where T_(d), equal to 1/f_(d), is the period of the natural oscillationof the driving mass, and the relation 0<A_(th)<A₀ applies (it should benoted that altogether similar considerations may be applied to athreshold of a negative value; also, it is possible to rectify thesinusoid, so as to have two measurements per oscillation period).

A well-defined relation between the time interval Δt and the oscillationamplitude A₀ thus exists; in other words, the measurement of the timeinterval Δt may be used to infer the oscillation amplitude A₀. However,this relation is in this case dependent upon the oscillation frequencyf_(d) of the driving movement, which, even though being a designparameter of the MEMS gyroscope 1, may be affected by manufacturingprocess spread, temperature variations or other factors.

An aspect of the present application thus envisages exploitation, formeasurement of the time interval Δt, of a derived clock signal ck, at ahigh frequency, which also depends on the oscillation frequency f_(d) ofthe driving movement (i.e., on the natural frequency of the mainoscillation mode).

In particular, for this derived clock signal ck, the following relationsapply:

f_(ck) = kf_(d); and $T_{ck} = {\frac{1}{f_{ck}} = \frac{1}{{kf}_{d}}}$where f_(ck) is the frequency of the derived clock signal ck, T_(ck) isthe period of the derived clock signal ck, and k is an appropriatemultiplicative factor that defines the value of the frequency f_(ck) ofthe derived clock signal ck starting from the oscillation frequencyf_(d).

It is consequently possible to measure the duration of the time intervalΔt by the frequency f_(ck) and obtain a correspondence between a countN, which indicates the number of periods T_(ck) of the derived clocksignal ck counted in the time interval Δt, and the oscillation amplitudeA₀ of the driving movement. In particular, using the expressions givenpreviously, the following relation may be obtained:

$N = {\frac{\Delta\; t}{T_{ck}} = {{\frac{f_{ck}}{f_{d}}\lbrack {\frac{1}{2} - {\frac{1}{\pi}{\sin^{- 1}( \frac{A_{th}}{A_{0}} )}}} \rbrack} = {k\lbrack {\frac{1}{2} - {\frac{1}{\pi}{\sin^{- 1}( \frac{A_{th}}{A_{0}} )}}} \rbrack}}}$

Basically, there is a well-defined relation between the count N (and theassociated duration of the time interval Δt) and the oscillationamplitude A₀, or, in other words, it is possible to infer the value ofthe aforesaid oscillation amplitude A₀ starting from count N. Inparticular, this count N is in no way dependent upon the oscillationfrequency f_(d) (and the possible associated spread or variations).

A control of the driving action based on the aforesaid count N to inferthe value of the oscillation amplitude A₀ may thus guaranteerepeatability of the amplitude value and of the associated detectionsensitivity of the MEMS gyroscope, even in the presence of possibleprocess spread or variations of the operating parameters causingvariations of the value of the driving frequency f_(d).

What has been previously discussed is confirmed by an analysis of theplots of FIGS. 4 and 5 , obtained via simulation, which show,respectively, the plot of the time interval Δt (FIG. 4 ) and of count N(FIG. 5 ), as a function of the ratio A_(th)/A₀ between the amplitudethreshold A_(th) and the oscillation amplitude A₀, at three differentvalues of the oscillation frequency f_(d), in the example, 19 kHz, 20kHz, and 21 kHz. The value of the multiplicative factor k is, in thesimulation, equal to 128, by way of example.

In particular, the aforesaid FIGS. 4 and 5 show that, as the oscillationfrequency f_(d) varies (in the example with a spread of approximately5%, in line with what could be expected from technological spread in anillustrative process), a corresponding variation of the duration of thetime interval Δt occurs for a given value of the ratio A_(th)/A₀,whereas, instead, the count N remains absolutely unvaried.

FIG. 6 further shows how the plot of count N varies as a function of theoscillation amplitude A₀, at three different values of the aforesaidmultiplicative factor k and of the resulting frequency f_(ck) (being 64,128, or 256 times the oscillation frequency f_(d)), further assuming, byway of example, an amplitude threshold A_(th) of 0.2 (it is to be notedthat the amplitude values are normalized to 1).

In particular, FIG. 6 shows that the resolution is higher (or,equivalently, the quantization error is lower) for high values of thefrequency f_(ck) of the derived clock signal ck and in the case wherethe value of the amplitude threshold A_(th) is close to the value of theoscillation amplitude A₀ of the drive signal V_(SD).

It thus follows that, at the design stage, once the desired value of theoscillation amplitude A₀ has been set, in so far as it depends on thecharacteristics of the micromechanical structure and the desireddetection sensitivity value for the MEMS gyroscope, it is possible toselect an appropriate value for the amplitude threshold A_(th) and themultiplicative factor k so as to define an optimal operating point forthe driving circuit, to which optimal values of the correspondingelectrical characteristics correspond. In this way, even smallvariations in the oscillation amplitude may advantageously be detected.

In particular, as previously mentioned, it is in general advantageousfor the operating point to satisfy one or both of the followingconditions: the ratio A₀/A_(th) is low (e.g., less than 2); themultiplicative factor k is high (e.g., greater than 128).

With reference to FIG. 7 , a description is now presented of a possibleembodiment of a driving circuit, designated in this case by 20, for aMEMS gyroscope, which exploits the solution described previously fordetermining a measurement of the oscillation amplitude of the drivingmovement of a corresponding mobile mass, and implementing, based on thismeasurement of the oscillation amplitude, feedback control of thedriving movement.

As it is clear from an examination of the aforesaid FIG. 7 , the drivingcircuit 20 basically corresponds to the driving circuit 14 describedwith reference to FIG. 2 ; consequently, elements that are similar aredesignated by the same reference numbers and are not described in detailany further.

The driving circuit 20 differs in that the AGC stage 18 is absent and isin this case replaced by a measurement stage 22, configured to perform ameasurement in the time domain, in a substantially digital manner, ofthe oscillation amplitude of the driving movement.

The above measurement stage 22 comprises a threshold-comparator block24, which receives at its input the drive signal V_(SD) generated by theinput stage 15 and generates at its output a time-over-threshold signalS_(ToT), i.e., a signal having a first value (e.g., a high value) if thedrive signal V_(SD) is higher than the amplitude threshold A_(th) (thevalue of which is appropriately set, as discussed previously) and asecond value (e.g., a low value), otherwise.

The threshold-comparator block 24 receives the amplitude thresholdA_(th) from a threshold-reference block 24′, configured to generate thesame amplitude threshold A_(th) with a precise and stable value, viaknown circuits, such as bandgap circuits that supply a stable and, whereused, adjustable voltage reference.

The measurement stage 22 further comprises a counter block 25, of adigital nature, coupled to the threshold-comparator block 24, from whichit receives the time-over-threshold signal S_(ToT), and further coupledto the PLL stage 17, from which it receives a derived clock signal ck atthe frequency f_(ck) (the value of which is appropriately set, asdiscussed previously). The counter block 25, enabled by thetime-over-threshold signal S_(ToT), is configured to determine the countN, i.e., the number of periods T_(ck) of the derived clock signal ckwithin the time interval Δt; this count number N, as discussedpreviously, is directly proportional to the oscillation amplitude A₀ ofthe driving movement.

In this regard, FIG. 8 shows, for a single half-cycle of the naturalclock signal ck: a semi-period of oscillation T_(d); thetime-over-threshold signal S_(ToT); and the derived clock signal ck atthe appropriate frequency f_(ck), windowed by the time-over-thresholdsignal, the number of cycles of which determines the count N fordetermining the duration of the time interval Δt. From FIG. 8 , it isclear that the resolution in the evaluation of the time over-thresholdis linked to the frequency f_(ck): the greater the multiplicative factork, the shorter the period T_(ck) of the derived clock signal ck and thusthe better the resolution measurement, or, in other words, the lower thequantization error introduced by the digital measurement of timeinterval Δt.

The driving circuit 20 further comprises a control stage 26, including,in this case, a digital-to-analog converter (DAC) block 27, whichreceives at its input the count N to determine the control signalV_(ctrl) for the forcing stage 19. In particular, the control stage 26is configured to determine the control signal V_(ctrl) based on theoscillation amplitude A₀ (measured by the previous expression thatuniquely links the oscillation amplitude A₀ to the count N) and theamplitude threshold A_(th).

As illustrated in FIG. 9 , a further embodiment may envisage thatforcing, i.e., the generation of the drive signals D₁, D₂, and thecorresponding driving feedback-control, are implemented by regulatingthe phase of the forcing signal maintaining the amplitude constant,instead of by regulating the amplitude as in the case of the previousembodiment.

In this regard, a phase-control technique for a MEMS gyroscope is, forexample, described in “Controlling the primary mode of gyroscopes with aphase-based amplitude regulation”, T. Northemann, et al., 2011Proceedings of the ESSCIRC (ESSCIRC), Sep. 12-16, 2011, pp. 295-298.

In this embodiment, the control stage, once again designated by 26,instead of supplying at its output the analog control signal V_(ctrl)for the forcing stage 19, i.e., an amplitude-control signal, isconfigured to implement a digital shifter 28, which supplies at itsoutput a properly delayed version (delayed clock Φ_(ctrl)) of the inputclock signal ck, where the delay is determined by the count N; thedigital shifter 28 also receives a suitable derived clock signal ck fromthe PLL stage 17.

The forcing stage 19 receives the delayed clock Φ_(ctrl) and, in thiscase, a forcing amplitude signal V_(force), having a pre-set value, forappropriately generating the phase of the drive signals D₁, D₂, which inthis case have a constant amplitude.

The above control solution has the advantage of not using adigital-to-analog conversion in the control stage 26, which implementsin fact forcing regulation in the digital domain, thus proving even morerobust in regard to possible process spread or variations of theoperating conditions.

The advantages of the solution proposed are clear from the foregoingdescription.

In any case, it is once again emphasized that the solution described isbased on a digital processing of the input signal to obtain theinformation on the oscillation amplitude of the driving mode, on whichthe driving feedback-control is based.

In particular, apart from the threshold-comparator block 24 and thethreshold-reference block 24′ that supplies the static reference thatdefines the amplitude threshold A_(th) (where these blocks may in anycase be conveniently designed and implemented, as regards thecorresponding stability and immunity to noise), this solution does notrequire analog processing blocks, as is instead required in a customaryAGC stage.

Second-order effects deriving from the drift of the analog values of theparameters (such as bandwidth and gain) are in this way eliminated ormarkedly reduced.

Furthermore, the robustness to temperature variations or to otherenvironmental conditions and to ageing effects is increased, andmeasurement of the oscillation amplitude is less susceptible to noise onthe input signal.

The solution described entails a lower current consumption as comparedto traditional solutions of a totally analog type, where a considerableelectrical consumption is used to limit the effects of the noise on theoutput measurement and to guarantee an adequate gain of the stageswithin the architecture.

Further, the present Applicant has found that the solution proposed isrobust also with respect to any offset on the value of the amplitudethreshold A_(th) used by the comparator block 24, since known circuittechniques may be implemented to eliminate the effects of the offset.

For instance, in a per se known manner, the chopping technique may beused in the comparator block 24 (a technique envisaging high-frequencymodulation of the input signal and subsequent demodulation by filtering)in order to reduce to substantially negligible levels the effects of thecomparator offset.

It is further emphasized that the appropriate choice of the operatingpoint of the comparator stage 24 enables the comparison with theamplitude threshold A_(th) to be made in an area of the drive signalV_(SD) having a steep slope, with the advantages that will be clear to aperson skilled in the sector.

Basically, the aforesaid characteristics make the resulting MEMSgyroscope particularly suitable for integration in an electronic device30, as shown schematically in FIG. 10 ; the electronic device 20 may beused in a plurality of electronic systems, for example in inertialnavigation systems, in automotive systems, or in systems of a portabletype, such as a PDA (Personal Digital Assistant), a portable computer, amobile phone, a digital audio player, and a photographic or videocamera, the electronic device 30 being generally capable of processing,storing, transmitting, and receiving signals and information.

The electronic device 30 comprises: the MEMS gyroscope, here designatedby 32, provided in particular with the driving circuit 20 configured todrive the mobile driving mass thereof; and an electronic control unit34, for example a microprocessor, a microcontroller, or a similarcomputing unit, which is connected to the driving circuit 20 and to thereading circuit 12 of the MEMS gyroscope 32, from which it receives theoutput voltage V_(out), and is configured to supervise general operationof the electronic device 30, also on the basis of the aforesaid outputvoltage V_(out), indicative of the detected angular velocity.

Finally, it is clear that modifications and variations may be made towhat has been described and illustrated herein, without therebydeparting from the scope of the present invention.

In general, it is emphasized that the present solution may be applied,obtaining similar advantages, also with different control strategies anddifferent forcing approaches of the micromechanical structure of theMEMS gyroscope (even different from what has been illustratedpreviously), which employ in any case a measurement of the oscillationamplitude of the driving movement.

In particular, the control stage 26 of the driving circuit 20 couldimplement a different solution for control of the forcing stage 19configured to supply the drive signals D₁, D₂ for the micromechanicalstructure of the MEMS gyroscope.

Furthermore, in the case where the input stage 15 supplies at its outputtwo differential drive signals, the comparator block 24 may also be of adifferential type, using two amplitude thresholds, a negative one and apositive one, for determining the time over-threshold, in a way that isotherwise altogether similar to what has been previously illustrated.

Finally, it is emphasized that the driving circuit 20 may advantageouslybe used with any configuration of the micromechanical structure of theMEMS gyroscope, in order to supply the biasing signals for driving acorresponding mobile driving mass. In particular, it is underlined inthis regard that what illustrated in FIG. 1 represents only anon-limiting exemplary embodiment of a possible micromechanicalstructure. For instance, in the micromechanical structure of the MEMSgyroscope a single mobile mass could be present, elastically supportedabove the substrate, so as to perform both the driving movement and thesensing movement as a result of the resulting Coriolis forces throughone and the same mobile mass.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

The invention claimed is:
 1. A driving circuit, comprising: ameasurement stage configured to: receive a signal representative of amovement of a microelectromechanical system (MEMS) mobile mass; anddetermine an oscillation amplitude of the movement of the MEMS mobilemass based on a number of periods of a clock signal that are in aduration of a time interval in which an amplitude of the signalsatisfies an amplitude criterion; and a control stage configured togenerate at least one drive signal for the MEMS mobile mass based on theoscillation amplitude, and output the at least one drive signal fordriving the MEMS mobile mass at an oscillation frequency.
 2. The drivingcircuit according to claim 1, wherein the measurement stage isconfigured to: generate the clock signal based on the oscillationfrequency.
 3. The driving circuit according to claim 2, wherein themeasurement stage is configured to: determine the duration of the timeinterval in which the signal satisfies the amplitude criterion.
 4. Thedriving circuit according to claim 1, wherein the number of periods ofthe clock signal that are in the duration of the time interval isdetermined as:${N = {\frac{\Delta\; t}{T_{ck}} = {{\frac{f_{ck}}{f_{d}}\lbrack {\frac{1}{2} - {\frac{1}{\pi}{\sin^{- 1}( \frac{A_{th}}{A_{0}} )}}} \rbrack} = {k\lbrack {\frac{1}{2} - {\frac{1}{\pi}{\sin^{- 1}( \frac{A_{th}}{A_{0}} )}}} \rbrack}}}},$wherein Δt is the duration of the time interval, T_(ck) is a period ofthe clock signal, f_(ck) is a frequency of the clock signal, f_(d) isthe oscillation frequency, k is a factor, and A_(th)/A₀ is a ratio of anamplitude threshold of the amplitude criterion and the oscillationamplitude.
 5. The driving circuit according to claim 1, wherein themeasurement stage includes: a threshold-comparator block configured tocompare the signal with an amplitude threshold, and generate atime-over-threshold signal indicative of the duration of the timeinterval during which an absolute value of the signal is above theamplitude threshold; and a counter block configured to determine thenumber of periods of the clock signal based on the time-over-thresholdsignal.
 6. The driving circuit according to claim 2, wherein the controlstage includes: a digital-to-analog converter configured to compare theoscillation amplitude with a reference value representing a desiredoscillation amplitude of the movement of the MEMS mobile mass, andgenerate a control signal based on comparing the oscillation amplitudewith the reference value and output the control signal.
 7. The drivingcircuit according to claim 1, wherein the control stage includes: adigital shifter configured to receive the number of periods of the clocksignal, generate, based on the number of periods of the clock signal, adelayed clock signal, and output the delayed clock signal.
 8. Thedriving circuit according to claim 5, wherein the absolute value of theamplitude threshold is greater than zero and less than an absolute valueof the oscillation amplitude.
 9. A microelectromechanical system (MEMS)device, comprising: a mobile mass; and a driving circuit including: ameasurement stage configured to: receive a signal representative of amovement of the mobile mass; and determine an oscillation amplitude ofthe movement of the mobile mass based on a number of periods of a clocksignal that are in a duration of a time interval in which an amplitudeof the signal satisfies an amplitude criterion; and a control stageconfigured to generate at least one drive signal for the mobile massbased on the oscillation amplitude, and output the at least one drivesignal for driving the mobile mass at an oscillation frequency.
 10. TheMEMS device according to claim 9, wherein the measurement stage isconfigured to: generate the clock signal based on the oscillationfrequency.
 11. The MEMS device according to claim 10, wherein themeasurement stage is configured to: determine the duration of the timeinterval in which the signal satisfies the amplitude criterion.
 12. TheMEMS device according to claim 9, wherein the number of periods of theclock signal that are in the duration of the time interval is determinedas:${N = {\frac{\Delta\; t}{T_{ck}} = {{\frac{f_{ck}}{f_{d}}\lbrack {\frac{1}{2} - {\frac{1}{\pi}{\sin^{- 1}( \frac{A_{th}}{A_{0}} )}}} \rbrack} = {k\lbrack {\frac{1}{2} - {\frac{1}{\pi}{\sin^{- 1}( \frac{A_{th}}{A_{0}} )}}} \rbrack}}}},$wherein Δt is the duration of the time interval, T_(ck) is a period ofthe clock signal, f_(ck) is a frequency of the clock signal, f_(d) isthe oscillation frequency, k is a factor, and A_(th)/A₀ is a ratio of anamplitude threshold of the amplitude criterion and the oscillationamplitude.
 13. The MEMS device according to claim 9, wherein themeasurement stage includes: a threshold-comparator block configured tocompare the signal with an amplitude threshold, and generate atime-over-threshold signal indicative of the duration of the timeinterval during which an absolute value of the signal is above theamplitude threshold; and a counter block configured to determine thenumber of periods of the clock signal based on the time-over-thresholdsignal.
 14. The MEMS device according to claim 10, wherein the controlstage includes: a digital-to-analog converter configured to compare theoscillation amplitude with a reference value representing a desiredoscillation amplitude of the movement of the mobile mass, and generate acontrol signal based on comparing the oscillation amplitude with thereference value and output the control signal.
 15. The MEMS deviceaccording to claim 9, wherein the control stage includes: a digitalshifter configured to receive the number of periods of the clock signal,generate, based on the number of periods of the clock signal, a delayedclock signal, and output the delayed clock signal.
 16. A method,comprising: receiving a signal representative of a movement of amicroelectromechanical system (MEMS) mobile mass; determining anoscillation amplitude of the movement of the MEMS mobile mass based on anumber of periods of a clock signal that are in a duration of a timeinterval in which an amplitude of the signal satisfies an amplitudecriterion; generating at least one drive signal for the MEMS mobile massbased on the oscillation amplitude; and outputting the at least onedrive signal for driving the MEMS mobile mass at an oscillationfrequency.
 17. The method according to claim 16, comprising: generatethe clock signal based on the oscillation frequency.
 18. The methodaccording to claim 16, comprising: determining the duration of the timeinterval in which the signal satisfies the amplitude criterion.